Attorney General Jeff Sessions announced Monday that the Justice Department will begin prosecuting every person who illegally crosses into the United States along the Southwest border,a hard-line policy shift focusing in particular on migrants traveling with children.

In separate speeches — one in Scottsdale, Ariz., the other in San Diego — Sessions said the Department of Homeland Security will begin referring such cases to the Justice Department for prosecution. Federal prosecutors will “take on as many of those cases as humanly possible until we get to 100 percent,” he said.

“If you cross the border unlawfully . . . then we will prosecute you,” Sessions said. “If you smuggle an illegal alien across the border, then we’ll prosecute you. . . . If you’re smuggling a child, then we’re going to prosecute you, and that child will be separated from you, probably, as required by law. If you don’t want your child separated, then don’t bring them across the border illegally. It’s not our fault that somebody does that.”

DHS officials say they have seen a significant increase in illegal border crossings over the past year, including a rise in the number of families and unaccompanied children. In the past month, Border Patrol officers say they have encountered more than 50,000 immigrants trying to enter the United States. From April 2017 to April 2018, the number of apprehensions and “inadmissible” border crossings tripled, according to DHS.

Advocates for migrants have said most are fleeing violence in Central America and should be treated as asylum seekers, not criminals. The American Civil Liberties Union has already filed a federal lawsuit in California over past separations.

A 4-year-old boy weeps in the arms of a family member after he and others were apprehended by U.S. Border Patrol agents upon crossing illegally near McAllen, Tex., on May 2. (Adrees Latif/Reuters)

Sessions indicated that while he has “no doubt” people illegally crossing the border are fleeing danger or despair, “We cannot take everyone on this planet who is in a difficult situation.”

California Attorney General Xavier Becerra (D), who has battled the Trump administration in court, signaled that he was following the issue closely.

“As a father, the last thing I would do is separate fathers and mothers from their children and I would hope the federal government thinks twice about doing this,” Becerra said. “There are constitutional protections we can look to.”

In San Diego, Sessions was interrupted by a heckler with a megaphone.

“We don’t want you in our state,” the man yelled. “Are you going to be separating families? Is that why you’re here? Why are you doing this? Do you have a heart? Do you have a soul? Why do you work for this administration?”

Senior immigration and border officials called for the increased prosecutions last month in a confidential memo to Homeland Security Secretary Kirstjen Nielsen. They said filing criminal charges against migrants, including parents traveling with children, would be the “most effective” way to tamp down on illegal border crossings.

The “zero-tolerance” measure announced Monday could split up thousands of families because children are not allowed in criminal jails. Until now, most families apprehended crossing the border illegally have been released to await civil deportation hearings.

The Trump administration piloted this approach in the Border Patrol’s El Paso sector, which includes New Mexico, between July and November 2017, and said the number of families attempting to cross illegally plunged by 64 percent.

The New York Times reported last month that hundreds of children have been taken from their parents at the border since October.

Nielsen told lawmakers in April that DHS aims to keep families together “as long as operationally possible.” She said families are separated to “protect the children” in case the adults traveling with them are not really their parents.

Sessions, who as attorney general has been especially aggressive on immigration, said that to carry out the new enforcement policies, he was sending 35 prosecutors to the Southwest and 18 immigration judges to the border to handle asylum claims. Those moves were announced last week.

Criminal prosecutions at the border have soared over the past two decades, from fewer than 10,000 cases in 1996 to more than 90,000 at their peak in 2013 under former president Barack Obama, according to TRAC, a Syracuse University organization that tracks criminal immigration prosecutions. Last fiscal year, the number of immigration prosecutions declined 14 percent, to nearly 60,000.

The most common criminal charge is “improper entry by alien” — or illegal entry. First-time offenders usually face a federal misdemeanor punishable by up to six months in prison or fines. Repeat offenders can be imprisoned for up to two years and fined, or charged with the more serious offense of “illegal reentry.”

After President Trump called last month for renewed efforts to reduce illegal border crossings, Sessions ordered U.S. attorneys on the border to prosecute migrants “to the extent practicable.” His remarks Monday appeared to signal that federal prosecutors will make this a higher priority.

“Eleven million people are already here illegally,” Sessions said in his speech. “That’s more than the population of the state of Georgia. . . . We’re not going to stand for this. We are not going to let this country be invaded. We will not be stampeded. We will not capitulate to lawlessness.”